Add script to document deleting private networks

In order to test clouds with no private networks, we need to delete
the ones made by devstack. This is how that works.

Change-Id: I6c9d4d62ea34372d53399aa2b8b27b762d53339b

extras/delete-network.sh

@@ -0,0 +1,14 @@
+neutron router-gateway-clear router1
+neutron router-interface-delete router1
+for subnet in private-subnet ipv6-private-subnet ; do
+    neutron router-interface-delete router1 $subnet
+    subnet_id=$(neutron subnet-show $subnet -f value -c id)
+    neutron port-list | grep $subnet_id | awk '{print $2}' | xargs -n1 neutron port-delete
+    neutron subnet-delete $subnet
+done
+neutron router-delete router1
+neutron net-delete private
+
+# Make the public network directly consumable
+neutron subnet-update public-subnet --enable-dhcp=True
+neutron net-update public --shared=True